A phase change-type memory element is disclosed in Japanese Patent Laid-Open No. 21740/1993. This phase change-type memory element utilizes, as a recording material, an electrically rewritable and erasable phase-change material, for example, a material which enables electrical switching between a substantially amorphous state and a substantially crystalline state or between different resistance states while maintaining the crystalline state.
The structure of the phase change-type memory element disclosed in Japanese Patent Laid-Open No. 21740/1993 is such that a recording material (a phase change material) is provided between electrodes, and an insulating layer with an opening having a predetermined size is interposed between the electrodes and the recording material. Upon the application of a set pulse across the electrodes, the phase state is brought to an ON state, and upon the application of a reset pulse, the phase state is returned to an OFF state. Since, however, the diameter of a current path formed in the recording material upon the application of voltage is as large as 2 to 3 μm, the volume of the phase change area is large. This poses a problem that a large current pulse is necessary as a reset pulse for returning the phase state from the ON state to the OFF state. Further, the recording material except for the phase change area should be in an amorphous state. This necessitates the production of the phase change-type memory element at a temperature at or below the crystallization temperature of the recording material. Therefore, for example, the temperature in the production of transistors or diodes constituting a drive circuit is disadvantageously restricted.
On the other hand, Japanese Patent Laid-Open No. 45583/1992 discloses a phase change-type memory element having a structure including an insulating layer having a contact hole having an inner diameter of 0.1 to 1.5 μm. A recording material layer is provided on one side of the insulating layer so as to fill the inside of the contact hole, and the recording material layer and the insulating layer are sandwiched between lower and upper electrodes. Further, Japanese Patent Laid-Open No. 45585/1992 discloses a phase change-type memory element including a recording material in a columnar form having a diameter of 0.1 to 1.5 μm provided between upper and lower electrodes. An insulating layer is provided on the periphery of the recording material.
In the phase change-type memory elements disclosed in Japanese Patent Laid-Open Nos. 45583/1992 and 45585/1992, the reset pulse current necessary for returning the phase state from an ON state to an OFF state is relatively small and there is no restriction on the process temperature. However, the formation of the contact hole having an inner diameter of 0.1 to 1.5 μm and the formation of a columnar recording material having a diameter of 0.1 to 1.5 μm requires advanced techniques, disadvantageously resulting in lowered yields. Further, there is a limit to the production technology for a reduction in inner diameter of the contact hole to be filled with the recording material or a reduction in diameter of the recording material. In the phase change-type memory elements having structures as disclosed in Japanese Patent Laid-Open Nos. 45583/1992 and 45585/1992, there is a limit to an improvement in integration density.